Magnetic Resonance Imaging of Hidradenitis Suppurativa: A Focus on the Anoperineal Location

Abstract

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease involving apocrine-bearing sites. It is characterized by recurrent painful nodules and abscesses that potentially rupture, resulting in sinus tract formation, fistulas, and scarring. HS tends to be found in the intertriginous areas (i.e., the axillary, inguinal, and perianal areas of the body). HS may be uncommon for radiologists because its diagnosis is usually based on clinical assessment. However, diagnosis based solely on clinical manifestations can underestimate the severity of HS. Ultrasonography and MRI play a critical adjunct role in determining the severity and extent of the disease and greatly aid its management. Given that MRI is an effective imaging tool, its role in the analysis of severe and anogenital HS lesions merits considerable attention. Unfortunately, anoperineal HS imposes diagnostic dilemmas. It has multiple symptoms and presentations and often mimics other diseases in the intertriginous areas. Therefore, a thorough understanding of HS is essential to avoid delayed diagnoses. This review highlights the typical MRI imaging features and staging of HS, emphasizing on the anoperineal location. The review also differentiates the disease from mimics to facilitate the prompt delivery of appropriate treatment and improve patients' quality of life.

Keywords: Anoperineal disease; Hidradenitis suppurativa; Imaging; MRI; Perianal disease.

Fig. 1. Bilateral axillary HS.

A, B. A 29-year-old female patient with bilateral axillary HS. Multiple erythematous papules (black arrows) and paired pits from inflamed hair follicles (white arrow) with dermal contractures and rope-like elevation of skin (white arrowhead) and bridging scar (black arrowheads) are shown at both axillae. Bilateral involvement is common in this disease. HS = hidradenitis suppurativa

Fig. 2. Step of progression in hidradenitis suppurativa.

Normal hair follicle with attached sebaceous gland (white arrowhead) is shown. Follicular occlusion causing widening of the hair follicle is observed (black arrow). Subsequently, there is a nodular or abscess formation (asterisk). Finally, there is interconnection of the abscesses (two asterisks) and then rupture. This can lead to the formation of a complex network of sinus tracts (black arrowheads). Skin thickening and induration (white arrows) develop during the course of the disease.

Fig. 3. Perineal hidradenitis suppurativa.

A 45-year-old male patient with tender and itching at perineum. Ultrasonography of the anterior perineum shows a few hypoechoic fluid pockets (asterisks). Widened dermal hair follicles connecting to fluid collection are seen (arrowheads). Several areas of hypodermal sinus tracts emanating from fluid collections are noted (arrows).

Fig. 4. Stage I hidradenitis suppurativa.

A 35-year-old female patient with painful lumps at right axilla. A. Coronal short tau inversion recovery image shows skin thickening or induration with evidence of subdermal high signal intensity (arrow). B. Coronal T1-weighted post gadolinium image shows area of enhancement extending to dermal surface at right axilla (arrow). Body marker was seen in both images.

Fig. 5. Stage I hidradenitis suppurativa.

A 51-year-old male patient with painful left groin. Axial short tau inversion recovery image shows skin thickening with subcutaneous abscess formation at left anterior perineum (arrow). Enlarged enhanced reactive bilateral inguinal nodes are identified (arrowheads).

Fig. 6. Stage II hidradenitis suppurativa.

A 35-year-old male patient with purulent discharge at perianal area. A. Axial short tau inversion recovery shows abscess pocket at left scrotum (asterisk) and multiple subdermal sinus tracts along right and left sided intergluteal cleft (arrowheads). Thickening of dermal plane and subcutaneous tissue of right gluteal region with increased signal intensity (arrow). B. DWI accentuates depiction of more subdermal sinus tracts (arrowheads) than axial short tau inversion recovery in (A). Skin and subcutaneous induration at right gluteal region is more conspicuous on DWI (arrow). DWI = diffusion-weighted image

Fig. 7. Stage II HS.

A 31-year-old male patient with grade II HS. Axial short tau inversion recovery shows multiple abscesses along right and left side of intergluteal cleft (white arrowheads) and sinus tract between abscesses at left side of intergluteal cleft (black arrowhead). Another branching sinus tract is in the left groin region (black arrow) with skin thickening and subcutaneous edema in the bilateral gluteal regions (white arrows). HS = hidradenitis suppurativa

Fig. 8. Stage III hidradenitis suppurativa.

A 37-year-old male patient with tender and foul discharge at perianal region. A. Axial short tau inversion recovery shows multiple subdermal sinus tracts along either side of the intergluteal cleft (white arrowheads). There is some intercommunication (black arrowheads) and marked subcutaneous thickening (black arrow) and a deep scar (white arrow). B. Axial short tau inversion recovery lower than (A) shows marked skin thickening (arrows) with scars and retracted skin surface at upper inner thighs (arrowheads). Significant scarring is very common in severe disease.

Fig. 9. Crohn’s disease and HS.

A. A 36-year-old male patient with Crohn’s disease and HS. Axial short tau inversion recovery shows subcutaneous abscess (arrowhead), subcutaneous induration with edema (white arrow), and enlarged inguinal nodes (N) consistent with HS. There is evidence of a perianal fistula in Crohn’s disease (black arrow). B. A 31-year-old male patient with Crohn’s disease and HS. Axial short tau inversion recovery shows subcutaneous abscess (white arrow) and sinus tract at left groin (white arrowhead), subcutaneous and skin thickening at left gluteal region (black arrowheads) and enlarged inguinal nodes consistent with HS (N) and associated perianal Crohn’s disease (black arrow). HS = hidradenitis suppurativa

Fig. 10. Pilonidal abscess.

A, B. A 37-year-old male patient with cutaneous discharge at mid upper buttock. Coronal short tau inversion recovery shows small focal high signal intensity at higher level of the intergluteal cleft (arrow) with elongated tract (arrowheads) in the left buttock and surrounding inflammatory change. There is no communication with the anal sphincteric area.

Fig. 11. Perineal actinomycosis.

A 32-year-old male patient with a history of penetrating trauma by wooden stick at left buttock. Axial T1-weighted post gadolinium image shows tract of penetrating trauma at medial aspect of left buttock. There is scrotal wall thickening with a rim enhancing abscess at the perineum (arrow). Fluid analysis of this abscess found actinomycosis.

Fig. 12. Fournier’s gangrene.

A 49-year-old male patient presented at the emergency unit with fever and tenderness of the genitalia. Axial enhanced CT shows soft-tissue edema and fascial thickening at scrotum and medial aspect of both upper thighs (arrows) and multiple soft-tissue gas (arrowheads). CT is far better than MRI for detecting air bubbles.

Fig. 13. Fournier’s gangrene.

A 52-year-old male patient with sepsis and multiple organ failure with crepitus at scrotal region. A. Axial fat-suppressed T2-weighted image shows skin thickening and subcutaneous edema at anterior perineal region (arrowheads). B. Axial fat-suppressed T2-weighted image shows marked scrotal wall thickening (arrows) and multiple tiny air bubbles at right scrotal sac (arrowheads).